Conventionally, fin-tube heat exchangers commonly have been used for various apparatuses such as air conditioners, freezer-refrigerators, and dehumidifiers. A fin-tube heat exchanger is composed of a plurality of fins that are arranged parallel to each other and spaced with a predetermined gap, and heat transfer tubes that extend through these fins.
Known fin-tube heat exchangers include ones with various ingenious fin shape designs so as to enhance heat transfer. For example, a heat exchanger in which a large number of pins are provided on a fin surface has been known. In this heat exchanger, the flow on the fin surface is stirred by these pins, so heat exchange is thereby enhanced.
However, providing the pins, which are different members from the fin, additionally on the fin complicates the manufacturing process. In view of this, a heat exchanger in which the fin shape is made ingenious by cutting and raising portions of the fin often is employed. For example, JP 2001-116488 A discloses a fin-tube heat exchanger in which a plurality of slit-shaped cut-and-lifts (hereinafter also referred to as “slit portions”) are formed. In this heat exchanger, the slit portions are formed by press-forming the fin so that the portions of the fin are cut and raised in a slit shape.
In a fin that has the slit portions (the fin is hereinafter also referred to as a “slit fin”), heat transfer is enhanced based on the following principle. In a fin 100 without the slit portions (flat fin), a continuous thermal boundary layer BL is produced from a front edge 100a of the fin 100 toward the rear when air A is supplied from the front, as illustrated in FIG. 12A. The thermal boundary layer BL is thin in the vicinity of the front edge 100a, but it gradually becomes thicker toward the rear. On the other hand, in a slit fin 101, as illustrated in FIG. 12B, the thermal boundary layer BL is produced not only from the front edge 101a of the fin 101 but also from each of the front edges 102a of the slit portions 102. Thus, it is possible to divide the thermal boundary layer BL from the front edge 101a of the fin 101 and to produce the thermal boundary layer BL discontinuously, as it were. Accordingly, the average thickness of the thermal boundary layer BL is thinner in the slit fin 101 than in the flat fin 100. As a result, heat transfer coefficient improves.